This invention relates generally to a washing machine controlled by a microcomputer, and more particularly to an operation control device for the washing machine including a host microcomputer and a sub microcomputer operated in response to a control command from the host microcomputer so that equipment such as a motor is controlled by these microcomputers in association.
Conventional washing machines are provided with a microcomputer-based operation control circuit. Control and operation equipment such as electromagnetic valves and a motor incorporated in the washing machine are controlled based on operation of the microcomputer. These equipment incorporated in the washing machine will be referred to as electrical equipment hereafter. A single microcomputer is usually provided in the conventional washing machine.
The cost of a one-chip microcomputer employed in the conventional washing machines has recently been increased progressively as the increases in the number of terminals and the memory capacity of the microcomputer. A plurality of, for example two, microcomputers have recently been employed in the washing machine for the purpose of cost reduction. In such a case a sub microcomputer controls the electrical equipment based on control commands from a host microcomputer.
However, the following defects can be found in the conventional washing machine employing a plurality of microcomputers. First, influences of noise or the like cause data error in the control commands transferred from the host microcomputer to the sub microcomputer as the increase in the number of microcomputers. Furthermore, the probability of occurrence of runaway of the microcomputers is increased. Consequently, the electrical equipment is abnormally operated and in the extreme, the washing machine runs into danger.
Second, if the runaway of the sub microcomputer should occur, a washing machine motor would keep running even when the operation command for running it is not supplied from the host microcomputer. In this case the washing machine motor could not be interrupted by the host microcomputer.
Third, where noise invades a transmission line during transmission of serial data between the computers or an error occurs in the output of the host microcomputer, the serial data lacks a plurality of bits thereof or error data invades the data on the transmission line. As the result of occurrence of such a situation, the subsequent serial data transfer timing is deviated by the lacked bits of data or increased data, resulting in change in the contents of the transferred data.